Adjustable flow control elements for balancing pulverized coal flow at coal pipe splitter junctions

ABSTRACT

An adjustable device installed at the inlet of conventional junctions/splitters ( 116 ) for on-line control of the distribution of coal among the outlet pipes is herein disclosed. The device includes a plurality of flow control elements ( 60 ) each positioned upstream of a plurality of flow channels in the riffler ( 50 ) for directing coal flow to the outlet pipes. Each flow control element preferably comprises a rounded convex edge leading to straight tapered sides (FIG.  9 ). The surfaces of the sides may be roughened or textured ( 63 ) for promoting turbulent boundary layers (FIG.  9 ). In addition, conventional fixed or variable orifices may be used in combination with the flow control elements for balancing primary air flow rates. The device allows fine-adjustment control of coal flow rates when used in combination with the slotted riffler, yet it has negligible effect on the distribution of primary air. The combination of the riffler assembly and the coal flow control elements ( 60 ) results in closely balanced coal flow. Balanced coal flow is imperative to the optimization of the operation of pulverized coal boiler systems (i.e. reduced pollutant emissions, improved combustion efficiency).

TECHNICAL FIELD

[0001] The invention relates to pulverized coal boiler systems and, moreparticularly, to riffler assembly and flow control element (e.g.adjustable air foil) designs for balancing the flows of pulverized coaltherein.

BACKGROUND ART

[0002] In a typical large pulverized coal boiler, coal particulate andprimary air flow from the pulverizers to the burners through a networkof fuel lines that are referred to as coal pipes.

[0003]FIG. 1 illustrates a typical large pulverized coal boilerinclusive of pulverizer(s) 10, furnace 30, and network of coal pipes 20.For proper operation of the boiler, all the coal pipes 20 connected toany one of the pulverizers 10 should carry the same coal flow rates andthe same flow rates of primary air.

[0004] Unfortunately, differences in coal and primary air flow ratesfrom one coal pipe 20 to the next are a limiting factor in the abilityto reduce NO_(X) emissions in pulverized coal boilers. High carbonmonoxide emissions and high levels of unburned carbon can result fromburner imbalances. High fly ash unburned carbon, in turn, can adverselyaffect electrostatic precipitator collection efficiency and result inelevated stack particulate emission levels. Imbalances in coal pipeflows can also lead to maintenance problems associated with coal pipeerosion and/or clogging (e.g. excessive localized coal accumulation),damage to burners and windboxes, and accelerated waterwall wastage.Problems such as these reduce the operating flexibility of the boilerand often require that the boiler be operated under conditions whichproduce higher NO_(X) levels than would otherwise be achieved.

[0005] The distribution of primary air throughout the coal pipingnetwork is controlled by the flow resistances of the various coal pipes20. Because of differences in pipe lengths and numbers and types ofelbows in each fuel line, the different coal pipes from a pulverizerwill usually have different flow resistances. It is known that orificesor flow restrictors can be installed within the pipes 20 for use inadjusting the individual primary air flows to make them equal.

[0006] For example, U.S. Pat. No. 5,593,131 to O. Briggs and J. Sundshows a Variable Orifice Plate for Coal Pipes for balancing coal pipeflows.

[0007] U.S. Pat. No. 5,685,240 to O. Briggs and J. Sund shows a VariableOrifice Plate for Coal Pipes.

[0008] U.S. Pat. No. 4,094,492 to R. Beeman and S. Brajkovich shows aVariable Orifice Using an Iris Shutter.

[0009] U.S. Pat. No. 4,779,546 to W. Walsh shows a Fuel Line Orifice.

[0010] U.S. Pat. No. 5,975,141 to M. Higazy shows an On-Line VariableOrifice.

[0011] U.S. Pat. No. 4,459,922 to R. Chadshay shows an ExternallyAdjustable Pipe Orifice Assembly.

[0012] It can be seen in the above-cited references that orifices withboth fixed geometry and adjustable geometry are available commercially.

[0013] While the use of fixed or adjustable orifices can be an effectiveway of balancing primary air flow rates, evidence from field andlaboratory measurements indicates the orifices have little effect oncoal flow rates. Instead, the coal flow distribution among the pipes isaffected most strongly by flow conditions and geometry in the inletregions of the pipes.

[0014]FIG. 2 illustrates a coal pipe 20 according to one pipingarrangement commonly encountered in pulverized coal boiler systems. Thisarrangement involves coal and primary air flow from one pipe 20 dividinginto two flows at a Y-shaped junction/splitter. Industry-wide experienceshows the coal flow rates among the two outlet pipes 22, 23 can beseverely imbalanced. More specifically, conventional orifices 40 a-b areinstalled to prevent primary air flow imbalance and the underlying tableshows the results from a series of laboratory tests carried out on theeffectiveness of orifices 40 a-b. As the data show, selection of theproper orifices 40 a-b as required to balance the primary air flow ratesdid not simultaneously result in a balanced coal flow distribution. Infact, in this case, the orifices 40 a-b increased the coal flowimbalance from 9.45% to 18.4%.

[0015] Another attempted solution for the coal flow imbalance is the useof adjustable baffles to modify the coal flow distribution among theoutlet pipes 22, 23. The following references describe the use ofbaffles to modify coal flow distribution.

[0016] U.S. Pat. No. 4,570,549 to N. Trozzi shows a Splitter for Usewith a Coal-Fired Furnace Utilizing a Low Load Burner.

[0017] U.S. Pat. No. 4,478,157 to R. Musto shows a Mill RecirculationSystem.

[0018] U.S. Pat. No. 4,412,496 to N. Trozzi shows a Combustion Systemand Method for a Coal-Fired Furnace Utilizing a Low Load Coal Burner.

[0019] In all of the above-described designs, the baffle is locatedupstream of the Y-junction and is used to control the relative amountsof coal flowing through the two outlet pipes 22, 23. This use ofadjustable baffles can be an effective way of modifying the distributionof the coal flow because the baffles can be adjusted to variouspositions. However, adjustment of the baffles also simultaneously causesunacceptably large changes in primary air flow distribution. As aconsequence, it is very difficult with an adjustable baffle approach tosimultaneously balance coal and primary air flow rates.

[0020] A third alternative comprises the insertion of a slotted rifflerin a splitter box as shown in FIG. 3 (prior art). The slotted rifflerconfiguration is also commercially used to reduce fuel flow imbalances.The slotted riffler concept consists of a series of flow channels withrectangular cross sections, each of which directs a portion of the coaland primary air flow to one of the outlet pipes. Field measurements showthat while these types of rifflers can help to reduce coal flowimbalance arising from a mal-distribution of coal flow at the inlet,they generally do not eliminate the imbalance. Additional fine controlof the coal flow distribution is still needed.

[0021] Often, due to the configuration of the boiler system, the flowfrom a single coal pipe must be split into more than two flows. FIG. 4shows an example of a four-way splitter arrangement 100 that issometimes encountered in pulverized coal boiler systems. The arrangement100 involves coal and primary air flow from a single pipe 102 dividinginto four flows at a four-way splitter 104. Industry experience showsthat the coal flow rates among the four outlet pipes 106 a-d can beseverely imbalanced. This is because the distribution of coal flow ratesamong the pipes 106 a-d strongly depends on the pulverized coal flowdistribution at the inlet cross-section of the four-way splitter 104,and a significant pulverized coal flow non-uniformity exists due to anupstream elbow 110. The non-uniformity causes the coal particles tostratify into a narrow localized stream (i.e. rope flow) close to theouter wall of the elbow 110. For this reason, a flow splitter must beinstalled either sufficiently far from an elbow or be designed toaccommodate significant coal flow non-uniformity. However, due to thespace limitations associated with many applications/installations, aflow splitter has to be installed immediately after an elbow where, asstated above, the coal particulate exists as a narrow, localized ropeflow.

[0022]FIG. 5 shows a sub-section of a known existing installation wherea Venturi 112 was installed between the exit of the elbow 114 and theinlet of the four-way splitter 116 in an attempt to lower inherent coalflow imbalances. Laboratory testing with this configuration showed a±35% coal flow imbalance among the four outlet pipes 118.

[0023] In the foregoing and all other known designs, theVenturi/restrictor(s) are fixed. The use of adjustable baffles would bea more effective way of modifying the distribution of the coal flowbecause the baffles can be adjusted to various positions. However,adjustment of baffles would also simultaneously cause unacceptably largechanges in primary air flow distribution. As a consequence, it is verydifficult with an adjustable baffle approach to simultaneously balancecoal and primary air flow rates.

[0024] It would, therefore, be advantageous to provide splitter designsthat eliminate coal flow imbalances at crucial points in a pulverizedcoal boiler system using an on-line adjustment capability (i.e. whilethe pulverized coal boiler system is in operation). This would permitthe operation of the pulverized coal boiler system to be optimized andresult in reduced pollutant emissions and improved combustionefficiency.

DISCLOSURE OF INVENTION

[0025] It is, therefore, the main object of the present invention toprovide an improved method and apparatus for the on-line balancing ofmultiple coal flows in a pulverized coal boiler system using a slottedriffler configuration, thereby making it possible to operate the boilersystem with reduced pollutant levels (e.g. NO_(x), CO) and increasedcombustion efficiencies.

[0026] It is another object of the present invention to provide animproved method and apparatus for the on-line balancing of multiple coalflows in a pulverized coal boiler system that does not disturb anypre-existing primary air flow balance among the multiple coal pipes.

[0027] It is a further object of the present invention to provide animproved method and apparatus for the on-line balancing of multiple coalflows in a pulverized coal boiler system at any of a two-way, three-way,and four-way splitter respectively having four outlet pipes.

[0028] It is a further object of the present invention to provide animproved method and apparatus for the on-line balancing of multiple coalflows in a pulverized coal boiler system that can be readily installedwithin the piping networks of existing pulverized coal power plants.

[0029] The above objects will become more readily apparent on anexamination of the following description and figures. In general, thepresent invention disclosed herein includes a new method and apparatusfor coal flow control at junctions/splitters common to some pulverizedcoal transfer systems at coal-fired power plants.

[0030] The present invention includes riffler assemblies designed tolower coal flow imbalance (i.e. restore uniform particulate flowdistribution). Furthermore, the present invention includes flow controlelements (e.g. a plurality of air foils) located just upstream of theriffler assembly to provide means for on-line coal flowadjustment/control. Each flow control element preferably comprises arounded, convex edge leading to straight tapered sides (the sidesurfaces may be roughened or textured to promote turbulent boundarylayers). The combination of the riffler assembly and the flow controlelements, making it possible to achieve on-line control of the flowdistribution, results in closely balanced coal flow in the outlet pipes.

BRIEF DESCRIPTION OF DRAWINGS

[0031] Other objects, features, and advantages of the present inventionwill become more apparent from the following detailed description of thepreferred embodiment and certain modifications thereof when takentogether with the accompanying drawings in which:

[0032]FIG. 1 illustrates a typical large pulverized coal boilerinclusive of pulverizer(s) 10, furnace 30, and network of coal pipes 20.

[0033]FIG. 2 illustrates a coal pipe 20 according to one typical pipingarrangement commonly encountered in pulverized coal boilers.

[0034]FIG. 3 illustrates a prior art slotted riffler in a splitter box.

[0035]FIG. 4 illustrates a multi-pipe arrangement 100 that is sometimesencountered in pulverized coal boiler systems.

[0036]FIG. 5 illustrates a sub-section of a multi-pipe arrangement wherea Venturi 112 has been installed.

[0037]FIG. 6 shows an array of long air foil-like flow control elements60, according to a first embodiment of the present invention, that areplaced just upstream of the inlet to a conventional riffler 50.

[0038]FIG. 7 illustrates the discrete riffler 50 channels (indicatedleft “L” and right “R”) with a pair of upstream flow control elements 60a and 60 b according to a first embodiment of the present invention.

[0039]FIG. 8 illustrates the transverse displacement of flow controlelements 60 a and 60 b to increase coal flow to the left side of theriffler 50.

[0040]FIG. 9 is a cross-section of the preferred shape of a single flowcontrol element 60 according to a first embodiment of the presentinvention.

[0041]FIG. 10 illustrates the width of the wake in the primary air flowdownstream of flow control element 60.

[0042]FIG. 11 shows the addition of roughness elements 63 for furtherreducing the width of the primary air wake (Wa).

[0043]FIG. 12 illustrates three examples of alternative flow controlelement shapes, each of which creates primary air and particle wakeshaving certain widths and other characteristics.

[0044]FIG. 13 is a plot of the particle trajectories downstream of flowcontrol element 60.

[0045]FIG. 14 is a graphical illustration of the particle concentrationwake (A) and primary air flow wake (B) which result from theabove-referenced flow control element 60 design.

[0046]FIG. 15 is a plot showing the effect of the lateral position Δy ofthe flow control elements 60 on the coal and primary air flowimbalances.

[0047]FIG. 16 shows a single four-way riffler element assembly 120according to an alternative embodiment of the present invention.

[0048]FIG. 17 shows the joining of two, four-way riffler elementassemblies 120 to form a sub-section of a complete four-way splitter.

[0049]FIGS. 18 and 19 are a perspective view and a top view,respectively, showing a complete four-way splitter 140 with four rifflerelement assemblies 120 joined as in FIG. 17.

[0050]FIGS. 20, 21 and 22 are a top view, side view and front view,respectively, of a square outlet coal pipe arrangement, utilized inpulverized coal boiler systems, that require the use of four-waysplitters.

[0051] FIGS. 23-26 are a top view, end view, front view, and bottom viewof an in-line outlet coal pipe arrangement.

[0052]FIG. 27 is an end view perspective of the complete four-waysplitter 140, including the first and second stage flow control elements122, 124, according to an alternative embodiment of the presentinvention.

[0053]FIG. 28 is a graphical representation of the results of a seriesof laboratory tests on the effect of the position of the first stageflow control element 122 on the coal flow balance within a four-waysplitter 140 designed in accordance with an alternative embodiment ofthe present invention.

[0054]FIG. 29 is a graphical representation of the results of a seriesof laboratory tests showing the coal flow balancing capability of afour-way splitter 140 designed in accordance with an alternativeembodiment of the present invention.

[0055]FIG. 30 is a graphical representation of the results of a seriesof laboratory tests demonstrating the effect of the position of thefirst and second stage flow control elements 122, 124 on thepre-existing primary air flow balance within a four-way splitter 140designed in accordance with an alternative embodiment of the presentinvention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0056] As described above, the distribution of primary air in most coalboilers must be controlled separately by use of orifice-typerestrictions in individual pipes. It is important for good combustionthat the mechanism for controlling the coal flow distribution havenegligible effect on the distribution of primary air. The presentinvention offers a solution in the form of adjustable flow controlelements installed at the inlet of a slotted riffler, for on-linecontrol of the distribution of coal among the outlet pipes. The flowcontrol elements create primary air and particle wakes, and thedistribution of pulverized coal and primary air to the coal boiler canbe manipulated by controlling the location, size and characteristics ofthe wakes via the flow control elements.

[0057] More specifically, and as shown in FIG. 6, one embodiment of thepresent invention consists of an array of long air foil-like flowcontrol elements 60 that are placed just upstream of the inlet to aconventional riffler 50. As described above, a conventional riffler 50(see FIG. 3) when used in a two-way splitter (see FIG. 2) directs theflow of primary air to either the left or right outlet pipe by alternateriffler flow channels. When flow control elements 60 are placed upstreamof riffler 50 and directly in-line with the internal walls of theriffler 50, the elements 60 have no effect on the coal flow distributionthrough the riffler 50. However, lateral movement of flow controlelements 60 causes a shift in the coal flow distribution through theriffler 50.

[0058]FIG. 7 illustrates the discrete riffler 50 channels (indicated asleft “L” and right “R”) with a pair of upstream flow control elements 60a and 60 b positioned in-line with the internal walls of the riffler 50.When the flow control elements 60 a and 60 b are moved sideways, eitherto the right or left, they cause a shift in the coal flow distributionthrough the riffler 50.

[0059] More specifically, FIG. 8 illustrates the selectiveright-displacement of flow control elements 60 a and 60 b to increasecoal flow to the left side of the riffler 50. Increasing amounts ofdisplacement Δy will cause an increase in coal flow to the left outletpipe L and a corresponding decrease in coal flow to the right outletpipe R.

[0060] An entire array of parallel flow-control elements 60 can beadjustably mounted on positioning rods (not shown) supported by bushingsin the outer walls of the piping system. This way, the selectivetransverse position Δy of all parallel flow-control elements 60 can besimultaneously adjusted from outside the pipe by sliding the positioningrods, in or out of the pipe, thereby permitting on-line control of thecoal flow distribution.

[0061] The individual flow control elements 60 preferably employ aparticular shape to ensure that the control of coal flow distributiondoes not affect the primary air flow distribution. For best performance,each element 60 preferably has a tear-drop shape similar to that shownin FIG. 9. The breadth b of upstream surface of element 60 is convex,with a circular or nearly-circular profile. The straight sides of theelement are tapered along their length at an angle α to an apex. Theprimary air flow creates boundary layers on the surfaces of the element60, thereby producing a wake region downstream. All of the physicaldimensions of the flow control element 60 combine to affect the natureof the wake.

[0062]FIG. 10 illustrates the width of the wake in primary air flowdownstream of element 60. With combined reference to FIGS. 9 and 10, thedimensions of the element 60 and magnitude of the average primary airvelocity in the coal pipe result in laminar boundary layers on thesidewalls of the element 60. Laminar boundary layers are particularlysusceptible to boundary layer separation for a sufficiently large angleα. Delaying the onset of separation to positions further downstream(larger x) reduces the width of the wake region (Wa) for the primary airflow. This reduces the effect of changes in position of the controlelement 60 on primary air flow distribution through the riffler 50.

[0063] The further addition of surface roughness on the tapered sidesurfaces of the elements 60 can trigger transition to turbulence. Thismoves the flow separation even further downstream and reduces the widthof the primary air wake (Wa) even more

[0064]FIG. 11 shows the addition of roughness elements 63 for furtherreducing the width of the primary air wake (Wa). Roughness elements 63may be any suitable sputter-coating on flow control element 60, ormachined ribs, grooves or the like. The roughness elements and/or othersurface textures reduce the width of the primary air wake (Wa) bydelaying flow separation.

[0065] It should be understood that flow control element shapes otherthan as indicated in FIGS. 6-11, and other element surfacecontours/textures can be used, depending on the application. The goal isthe creation and control of a wake region. Other shapes create wakeshaving different sizes and characteristics. Consequently, certain othershapes may be well suited for certain other purposes. For example, FIG.12 illustrates three examples of alternative flow control elementshapes: a blunt leading edge (top); a wedge leading edge (middle); andcurved surfaces (bottom). Each of the alternative shapes of FIG. 12create primary air and particle wakes having certain widths and othercharacteristics.

[0066]FIG. 13 is a plot of the coal particle trajectories downstream offlow control element 60. As seen in FIG. 13, the width of the particlewake (Wp) is controlled by the particle size distribution, the velocityof upstream flow, the width b (as in FIG. 9) of element 60, and theshape of the upstream surface of the element 60. The rounded, convexshape of flow control element 60 is presently preferred because itprovides a smooth match with the straight tapered side walls of the coalpipe 20. The width b of element 60 is limited by the widths of the flowchannels in riffler 50. For the typical particle sizes and flowvelocities which occur in coal pipes in pulverized coal boilers, thewidth of the particle wake is larger in magnitude than the width b ofelement 60 as shown in FIG. 9.

[0067]FIG. 14 is a graphical illustration of the particle concentrationwake (A) and primary air flow wake (B) which result from theabove-referenced flow control element 60 design. It can be seen that theparticle wake causes a bell-curve reduction in particle flow across awidth Wp that exceeds the width b of the flow control element 60. On theother hand, the primary air flow wake causes only a minor interruptionin primary air flow across a width Wa that is smaller than the width bof the flow control element 60. Thus, the elements 60 have a negligibleeffect on the distribution of primary air and this eliminates the needfor separate control of orifice-type restrictions in individual pipes.

[0068] Laboratory tests have been conducted which demonstrate theeffectiveness of the above-described invention in controlling coal flowdistribution, without affecting primary air flow distribution. Thesetests were carried out with a 6″ inlet pipe and two 4″ outlet pipes. Theinlet air velocity was 100 feet per second (fps) and the ratio of themass flow rate of pulverized coal to the mass flow rate of air was 0.7.

[0069]FIG. 15 is a plot of test results showing the effect of thelateral position Δy of the flow control elements 60 on the coal andprimary air flow imbalances. The data show small adjustments in flowcontrol element position Δy resulted in large changes in coal flowdistribution, but almost no change in primary air flow distribution.

[0070] Other common configurations found in coal boiler systems splitthe flow of coal/primary air from one inlet pipe into three or fouroutlet pipes by use of a riffler assembly. The same above-describedapproach of adjustable air foil elements if used in combination with aslotted riffler can be applied in these cases to control thedistribution of coal flow among the outlet pipes.

[0071]FIG. 16 shows a single four-way riffler element assembly 120 thatsplits the flow of coal/primary air into four outlet flow channels 128.The riffler element assembly 120 of FIG. 16 incorporates a flow controlassembly with two stages of flow control elements 122, 124 according toan alternative embodiment of the present invention. In the illustratedembodiment, the four-way riffler element assembly 120 includes an inletflow channel 125 (not shown in FIG. 16, see FIG. 21) for creating flowas shown by directional arrow 126, two intermediate flow channels 127,and four outlet flow channels 128. The two-stage flow control assemblyincludes a first stage flow control element 122 and two second stageflow control elements 124. Each of the three flow control elements 122,124 is adjustable sideways from a ‘neutral’ position (aligned with thewall of its corresponding channel). All flow control elements in eachrespective stage 122 and 124 may be adjusted in tandem by mounting rodsas will be described. The coal/primary air mixture flows through theinlet channel 125 and around the first stage flow control element 122.The element 122 distributes the coal/primary air mixture into theintermediate flow channels 127 where it flows around the second stageflow control elements 124. These elements 124 further distribute themixture into the outlet flow channels 128.

[0072]FIG. 17 shows the side-by-side joining of two, four-way rifflerelement assemblies 120 as in FIG. 16 plus a respective pair of two-stageflow control assemblies both including a first stage flow controlelement 122 and two second stage flow control elements 124, to therebyform a complete four-way splitter.

[0073]FIGS. 18 and 19 are a perspective view and a top view,respectively, showing a complete four-way splitter 140 including thehousing 142 and four riffler element assemblies 120 joined as in FIG.17.

[0074]FIGS. 20, 21 and 22 are a top view, side view and front view,respectively, of another example of a square outlet coal pipearrangement, utilized in pulverized coal boiler systems, that requirethe use of four-way splitters.

[0075] FIGS. 23-26 are a top view, end view, front view, and bottom viewof an in-line arrangement. Factors such as the pre-existing layout ofthe coal/primary air mixture delivery system dictate which of thepossible outlet pipe arrangements can be implemented.

[0076]FIG. 27 shows the relative positions of the first and second stageflow control elements 122, 124, respective mounting rods 131, 132 fortandem adjustment, and the inlet, intermediate, and outlet flow channels125, 127, 128. It can be readily seen how the present invention achievescoal flow control in a two stage process. Flow from the inlet flowchannel 125 is passed by the first stage flow control element 122 inorder to convert the single flow into two, approximately equal coalflows through the two intermediate flow channels 127. Generally, the twointermediate flows are each then passed by the second stage controlelements 124 in order to convert the two intermediate flows into four,approximately equal coal flows, which are in turn directed into each offour discrete channels of a riffler element assembly to accomplishbalanced coal flows among all outlet pipes thereof. Moreover, theapparatus for the on-line balancing is simple in construction, containsa small number of individual components, and can be provided as originalequipment or designed to readily retrofit a large number of existingpulverized coal boiler systems without excessive modification.

[0077] More specifically, the first stage flow control elements 122(attached to mounting rod 131) are for balancing coal flows in theintermediate channels 127 (those designated “M” and “N”). The secondstage flow control elements 124 (two sets that are independentlyadjustable via two sets of mounting rods 132) are for balancing coalflows in the outlet pipes 128. The positions of the flow controlelements 122, 124 with respect to each other (i.e. along the mountingrods 131, 132), and the distance from them to the leading edges of theflow channel walls (shown as dimensions “D1” and “D2”) are selected soas not to disturb the primary air flow balance in any of the outletpipes 128 as the position of the flow controller elements 122, 124 areadjusted by sliding the mounting rods 131, 132 to the left or right (asoriented in FIG. 23).

[0078] The mounting rods 131, 132 are accessible during any normaloperating cycle of the pulverized coal boiler assembly. This providesfor the opportunity to make “on-line” adjustments to the positions ofthe first and second stage flow control elements 122, 124 during normaloperation of the boiler system. On-line adjustments allow the operationof the boiler system to be optimized independently of other surroundingconditions.

[0079] Referring back to FIG. 9, the preferred cross-section of the flowcontrol elements 122, 124 as in FIGS. 17 and 27 is likewise cone-shapedwith a convex, rounded leading surface possessing a width “b” that isproportional to the width of the flow channel in which it is positioned.Downstream of the flow control elements 122, 124, the coal flow createsa wider wake than that of the primary air flow. In other words, theprimary air flow is only slightly affected by the streamlined design ofthe flow control elements 122, 124. Laboratory tests have demonstratedthe effectiveness of the foregoing device in adjusting coal flowdistribution without affecting primary air flow distribution. Tests werecarried out with a single 6″ inlet pipe and four 3¼″ outlet pipes. Theinlet air velocity was set at 75 feet per second (fps) and the ratio ofthe primary air mass flow rate to the coal mass flow rate was 1.7. Theamount of flow imbalance is defined as the flow rate differentialbetween the measured flow in a pipe and the average flow rate that wouldcreate perfectly balanced flow among the four outlet pipes, divided bythat same average flow rate. Therefore, the amount of flow imbalance ata four-way splitter can be mathematically expressed as:$I_{i} = \frac{m_{i} - m_{avg}}{m_{avg}}$

[0080] Where the term m_(i) represents the measured flow rate in thei^(th) outlet pipe and the term m_(avg) is the average flow ratecalculated as follows:$m_{avg} = \frac{m_{1} + m_{2} + m_{3} + m_{4}}{4}$

[0081]FIG. 28 plots the effect of the position of the first stage flowcontrol elements 122 on coal flow balance between the intermediatechannels 127 designated (in FIG. 27) with an “M” and those marked withan “N”. As the first stage flow control elements 122 were moved towardsthe left (as seen in FIG. 27), less coal flowed to the “M” channels,resulting in negative coal flow imbalances for the “M” channels (asshown by the solid line in FIG. 28). In a similar fashion, as the firststage flow control elements 122 were moved towards the right, less coalflowed to the “N” channels, resulting in negative coal flow imbalancesfor the “N”channels (as shown by the dotted line in FIG. 28). With theflow control elements 122 positioned 0.04″ to the right of the neutralposition shown in FIG. 27, the coal flows to all of the intermediatechannels 127 were perfectly balanced.

[0082] It should be mentioned that this 0.04″ from neutral position forthe first stage elements 122 does not guarantee balanced coal flowbetween the various outlet pipes 128 designated (in FIG. 27) with “1”,“2”, “3”, and “4”. To accomplish balanced coal flows among all outletpipes 128, the second stage flow control elements 124 must also bepositioned properly.

[0083] The results of several laboratory trials are illustrated in FIG.29. Test no. 1 shows the coal flow imbalance for the four outlet pipesusing the four-way splitter configuration shown in FIG. 5 (i.e. withoutfour-way riffler element assemblies and flow control elements). Test no.2 shows the results obtained by using the present invention with theflow control elements 122, 124 located at the neutral positions shown inFIG. 27 (i.e. aligned with the walls of the intermediate and outlet flowchannels). A comparison of Test nos. 1 and 2 indicates that the coalflow imbalance was reduced from ±35% to ±13% by using the new four-waysplitter. A series of changes in the positions of the flow controlelements 122, 124 are reflected in the results of Test nos. 3 through 6.Note that Test no. 6 shows nearly perfect coal flow balance among thefour outlet pipes, a reduction in coal flow imbalance to less than ±4%.

[0084]FIG. 30 plots the primary air flow imbalance present during eachof the last five coal flow tests recorded in FIG. 29 (i.e. Test nos. 2through 6). As is readily apparent from the five sets of data shown inFIG. 30, any change in the positions of the flow control elements 122,124 has only a slight effect on the pre-existing primary air flowimbalance.

[0085] It is noteworthy that in some piping arrangements, thecoal/primary air flow from a single pipe is split into three, four, fiveor more outlet streams. It should be understood that the presentinvention encompasses system configurations in addition to thosedescribed above (for two or four outlet pipes), for instance, whichcombine adjustable flow control elements with a slotted riffler utilizedto control the distribution of coal flow among three outlet pipes, fiveoutlet pipes or any number of outlet pipes.

INDUSTRIAL APPLICABILITY

[0086] Typical pulverized coal boiler systems have internal imbalancesdue to upstream obstructions (e.g. one or more elbows). Thus, thepulverized coal flow at the inlet of a conventional two- or four-wayjunction/splitter possesses a non-uniform distribution. Prior artjunctions/splitters typically utilize orifices, adjustable baffles orriffler assemblies to reduce the effects of inlet flow non-uniformity onthe overall coal flow balance. Unfortunately, these conventionalapproaches generally do not eliminate imbalances. There would be greatcommercial advantage in a device that substantially eliminatesimbalances, and such a device is herein disclosed in the context of two-and four-way riffler assemblies designed to lower coal flow imbalance(i.e. restore uniform particulate flow distribution). Furthermore, therewould be great commercial advantage in a device that provides controlover imbalances, and the present invention further includes flow controlelements (e.g. a plurality of air foils) located just upstream of theriffler assembly to provide means for on-line coal flowadjustment/control. The combination of the riffler assembly and the flowcontrol elements makes it possible to achieve on-line control of theflow distribution, thus resulting in closely balanced coal flow in theoutlet pipes.

1. In combination with a slotted plate riffler having flow channels fordirecting coal flow and balancing coal flow rates among a plurality ofoutlet pipes from a splitter junction in a pulverized coal boilersystem, a flow control assembly including a plurality of flow controlelements each positioned upstream of a corresponding flow channel insaid riffler for creating a particle wake and thereby preferentiallydirecting coal flow to one of said plurality of outlet pipes from thesplitter junction.
 2. The combination slotted plate riffler and flowcontrol assembly according to claim 1, wherein said slotted plateriffler further comprising an orifice in each of said plurality ofoutlet pipes for balancing primary air flow rates.
 3. The combinationslotted plate riffler and flow control assembly according to claim 1,wherein said plurality of flow control elements of the flow controlassembly each further comprise a rounded convex edge leading to straighttapered sides.
 4. The combination slotted plate riffler and flow controlassembly according to claim 3, wherein the straight tapered sides ofsaid plurality of flow control elements each further comprise aroughened surface for promoting turbulent boundary layers.
 5. Thecombination slotted plate riffler and flow control assembly according toclaim 1, wherein said plurality of flow control elements are mounted onmeans to adjust the positions of said flow control elements relative tosaid riffler flow channels.
 6. The combination of a slotted plateriffler and a plurality of flow control elements according to claim 5,wherein said flow control assembly further includes means for adjustingsaid plurality of flow control elements relative to said riffler flowchannels.
 7. A system for balancing coal flow, without disturbingprimary air flow, at a splitter junction of a pulverized coal boilersystem, comprising: a plurality of first stage flow control elementslocated upstream of said splitter junction for converting a combinedcoal/primary air flow into a plurality of substantially equal coalflows; a plurality of discrete first channels for intake of theplurality of respective coal and air flows; a plurality of second stageflow control elements located within said plurality of discrete channelsfor converting said plurality of secondary stage air and coal flows intoa plurality of approximately equal, third stage coal flows; and aplurality of discrete second channels located downstream of saidplurality of second stage flow control elements for intake of theplurality of third stage coal flows.
 8. The system for balancing coalflow according to claim 7, further comprising an orifice in each of saidfour or more outlet pipes for balancing primary air flow rates.
 9. Thesystem for balancing coal flow in pulverized coal boiler systems withsplitter junctions having a single inlet coal pipe and a plurality ofoutlet coal pipes according to claim 7, wherein said pluralities offirst stage and second stage flow control elements each further comprisea rounded convex edge leading to straight tapered sides.
 10. The systemfor balancing coal flow in pulverized coal boiler systems with splitterjunctions having a single inlet coal pipe and a plurality of outlet coalpipes according to claim 9, wherein the straight tapered sides of saidpluralities of first stage and second stage flow control elements eachfurther comprise a roughened surface for promoting turbulent boundarylayers.
 11. The system for balancing coal flow in pulverized coal boilersystems with splitter junctions having a single inlet coal pipe and aplurality of outlet coal pipes according to claim 7, further comprisingmeans to adjust the positions of said pluralities of first stage andsecond stage flow control elements.
 12. The system for balancing coalflow in pulverized coal boiler systems with splitter junctions having asingle inlet coal pipe and a plurality of outlet coal pipes according toclaim 11, further comprising means to adjust the positions of saidpluralities of first stage and second stage flow control elements“on-line”, or in other words, while the boiler system is in operation.13. In a slotted plate riffler having a plurality of flow channels, amethod for directing coal flow and balancing coal flow rates among aplurality of outlet pipes from a splitter junction in a pulverized coalboiler system, comprising the steps of: passing a combined coal/primaryair flow over a plurality of flow control elements, each positionedupstream of said plurality of flow channels in said riffler, in order toconvert said combined flow into a plurality of approximately equalcoal/primary air flows, and; directing each of said plurality ofapproximately equal coal/primary air flows preferentially into aplurality of discrete flow channels of a riffler assembly;
 14. Themethod for directing coal flow and balancing coal flow rates among aplurality of outlet pipes from a splitter junction in a pulverized coalboiler system according to claim 13, wherein the positions of saidplurality of flow control elements are adjusted in order to furtherrefine/enhance the balancing effect.
 15. The method for directing coalflow and balancing coal flow rates among a plurality of outlet pipesfrom a splitter junction in a pulverized coal boiler system according toclaim 14, wherein the positions of said plurality of flow controlelements are adjusted “on-line”, or in other words, while the boilersystem is in operation to further refine/enhance the balancing effect.16. A method of balancing coal flow, without disturbing an existingprimary air flow, in pulverized coal boiler systems with splitterjunctions having a single inlet coal pipe and a plurality of outlet coalpipes, comprising the steps of: passing a combined coal/primary air flowover a plurality of first stage flow control elements in order toconvert said combined flow into a plurality of approximately equalcoal/primary air flows; directing each of said plurality ofapproximately equal coal/primary air flows preferentially into aplurality of first stage discrete channels of a riffler assembly;passing the plurality of approximately equal coal/primary air flows overa plurality of second stage flow control elements located within saidplurality of first discrete channels in order to convert said pluralityof approximately equal second stage coal/primary air flows into aplurality of approximately equal third stage coal/primary flows;directing each of said plurality of approximately equal third stagecoal/primary flows preferentially into a plurality of second discretechannels of a riffler assembly.
 17. The method of balancing coal flow,without disturbing an existing primary air flow, in pulverized coalboiler systems with splitter junctions having a single inlet coal pipeand a plurality of outlet coal pipes according to claim 16, wherein thepositions of said pluralities of first stage and second stage flowcontrol elements are adjusted in order to further refine/enhance thebalancing effect.
 18. The method of balancing coal flow, withoutdisturbing an existing primary air flow, in pulverized coal boilersystems with splitter junctions having a single inlet coal pipe and aplurality of outlet coal pipes according to claim 17, wherein thepositions of said pluralities of first stage and second stage flowcontrol elements are adjusted “on-line”, or in other words, while theboiler system is in operation to further refine/enhance the balancingeffect.